By law, most buildings need to have certain areas that are handicap accessible. While there are some ways to work around this if you have a historical building and such, newer buildings are mandated to have certain accommodations for those who may be wheelchair bound. While it may take a bit of extra work and planning on your end, taking handicap accessibility into consideration can help you immensely down the road.
The first thing that comes to mind when most people say "Handicapped" in regards to accessibility is parking. This should be something at the front of your mind as well if you are planning on modifying your rental property to accommodate those who may be less mobile. Having close parking that is specifically for those who are handicapped is something that you normally need to speak to the town about, however it usually is not a problem. Those who may need the accommodations are always extremely thankful for the proximity parking and this will reflect well on you even from those who don't have the need to use it. This shows that you care about those who you may rent to, regardless of any disability they may life with.
The second thing that you need to think about, and possibly fix, on a property you are meaning to rent out to someone who may be disabled is front door accessibility. While it's wonderful if they have preferred parking, that won't help if there are stairs or ridges that need to be dealt with. Having a ramp put in to allow access to an entrance and exit is always a good idea, however in this case it is essential. Also be careful to make sure there are no lips at the doorways that could cause problems for a wheelchair if someone were to try to bring one across the threshold. Also, they can be trip hazards, so even if you are not thinking of letting it out to someone disabled, perhaps try and take the ridge or bump out to lessen your liability.
There are many more things to be considered and they will be talked about in the next article. For now, think about the properties that you have and if any of these fixes could be made to your buildings. Even if you don't have any disabled residents, perhaps someone who you rent to has family that cannot access the apartment. Again, it can only help you to increase your accessibility.